Large scale production of thinned graphite, graphene, and graphite-graphene composites

ABSTRACT

Embodiments described herein relate generally to large scale synthesis of thinned graphite and in particular, few layers of graphene sheets and graphene-graphite composites. In some embodiments, a method for producing thinned crystalline graphite from precursor crystalline graphite using wet ball milling processes is disclosed herein. The method includes transferring crystalline graphite into a ball milling vessel that includes a grinding media. A first and a second solvent are transferred into the ball milling vessel and the ball milling vessel is rotated to cause the shearing of layers of the crystalline graphite to produce thinned crystalline graphite.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/409,153, filed May 10, 2019, now U.S. Pat. No. 11,367,540, entitled“LARGE SCALE PRODUCTION OF THINNED GRAPHITE, GRAPHENE, ANDGRAPHITE-GRAPHENE COMPOSITES,” which is a continuation of U.S. patentapplication Ser. No. 15/270,855, filed Sep. 20, 2016, now U.S. Pat. No.10,322,935, entitled “LARGE SCALE PRODUCTION OF THINNED GRAPHITE,GRAPHENE, AND GRAPHITE-GRAPHENE COMPOSITES,” which is a continuation ofU.S. patent application Ser. No. 14/978,566, filed Dec. 22, 2015, nowU.S. Pat. No. 9,469,542, entitled “LARGE SCALE PRODUCTION OF THINNEDGRAPHITE, GRAPHENE, AND GRAPHITE-GRAPHENE COMPOSITES,” which is acontinuation of International Patent Application No. PCT/CA2015/050525,filed Jun. 8, 2015, entitled “LARGE SCALE PRODUCTION OF THINNEDGRAPHITE, GRAPHENE, AND GRAPHITE-GRAPHENE COMPOSITES,” which claimspriority to and the benefit of U.S. Provisional Patent Application No.62/008,729, filed Jun. 6, 2014, entitled “Large Scale Production ofLarge Sheets of Few or Multi-Layer Graphene,” and U.S. ProvisionalPatent Application No. 62/035,963, filed Aug. 11, 2014, entitled “LargeScale Production of Thinned Graphite and Graphite-Graphene Composites,”the disclosures of which are hereby incorporated by reference in theirentirety.

BACKGROUND

Graphene is a single, one atomic layer of carbon atoms with severalexceptional electrical, mechanical, optical, and electrochemicalproperties, earning it the nickname “the wonder material.” To name justa few, it is highly transparent, extremely light and flexible yetrobust, and an excellent electrical and thermal conductor. Suchextraordinary properties render graphene and related thinned graphitematerials as promising candidates for a diverse set of applicationsranging from energy efficient airplanes to extendable electronic papers.For example, graphene based batteries may allow electric cars to drivelonger and smart phones to charge faster. As further examples, graphenecan also filter salt, heavy metals, and oil from water, efficientlyconvert solar energy, and when used as coatings, prevent steel andaluminum from rusting. In the longer term, thinned crystalline graphitein general promises to give rise to new computational paradigms andrevolutionary medical applications, including artificial retinas andbrain electrodes.

SUMMARY

Embodiments described herein relate generally to large scale synthesisof thinned graphite and in particular, few layers of graphene sheets andgraphene-graphite composites. In some embodiments, a method forproducing thinned crystalline graphite from precursor crystallinegraphite using wet ball milling processes is disclosed herein. Themethod includes transferring crystalline graphite into a ball millingvessel that includes a grinding media. A first and a second solvent aretransferred into the ball milling vessel and the ball milling vessel isrotated to cause the shearing of layers of the crystalline graphite toproduce thinned crystalline graphite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flowchart illustrating a method of producingthinned crystalline graphite, graphene and/or a graphene-graphitecomposite via a wet ball milling process, according to an embodiment.

FIGS. 2A and 2B show example schematics of the process of wet ballmilling in a ball milling vessel containing graphite, grinding media anda liquid solution, according to an embodiment.

FIG. 3 is an atomic force microscopy image of thinned crystallinegraphite produced via a wet ball milling process, according to anembodiment.

FIGS. 4A and 4B show top view (FIG. 4A) and cross-sectional view (FIG.4B) of a scanning electron microscope (SEM) micrograph of agraphene-graphite composite produced via a wet ball milling process,according to an embodiment.

FIG. 5 is a plot of thermogravimetric analysis illustrating the thermalstability of commercial graphene, exfoliated graphene, and thinnedgraphite produced via a wet ball milling process, according to anembodiment.

FIG. 6 is a plot of-thermogravimetric analysis illustrating the thermalstability of natural graphene, graphite and a graphene-graphitecomposite produced via a wet ball milling process, according to someembodiments.

FIG. 7 are plots of Fourier transform infrared spectroscopy ofsilicon-graphene (top panel) and titanium dioxide-graphene (bottompanel) composites representing a high degree of dispersion, according toan embodiment.

FIGS. 8A-8F are a series of SEM micrographs of a wide variety offew-layer graphene and graphene-graphite composites, according to anembodiment.

FIGS. 9A and 9B are plots of the lateral size distribution ofgraphene-based particles that comprise few-layer graphene samples,according to an embodiment.

FIG. 10 is a plot of Raman spectra for a series of different few-layergraphene, graphene-graphite composite, and bulk graphite, according toan embodiment.

FIGS. 11A-11G are plots showing the two peak deconvolution of the Ramanspectra of different few-layer graphene, graphene-graphite composite,and bulk graphite indicating the presence of a plurality of graphenelayers, according to an embodiment.

FIGS. 12A and 12B are plots showing the shift of the 2D band peak as afunction of the thickness of few-layer graphene samples, according to anembodiment.

FIG. 13 is alternative plot providing a compact view of the number oflayers in few-layer graphene samples and graphene-graphite composites,according to an embodiment.

FIG. 14 is a plot showing simulated results of the number of layers infew-layer graphene samples and graphene-graphite composites, accordingto an embodiment.

FIGS. 15A-15F are example plots of X-ray photon spectroscopy (XPS)spectra for a series of different few-layer graphene, graphene-graphitecomposite and bulk graphite, according to an embodiment.

FIG. 16 a plot of example Fourier transform infrared spectroscopy byattenuated total reflection (ATR-FTIR) spectra for a series of differentfew-layer graphene and bulk graphite, according to an embodiment.

FIG. 17 a plot of example Fourier transform infrared spectroscopy byattenuated total reflection (ATR-FTIR) spectra for a graphene-graphitecomposite, according to an embodiment.

FIG. 18 is a plot showing the results of thermo gravimetric analysis ofdifferent few-layer graphene, graphene-graphite composite and bulkgraphite indicating the thermal stability of these graphene-basedmaterials.

DETAILED DESCRIPTION

Embodiments described herein relate generally to large scale synthesisof thinned graphite, and in particular, few layers of graphene sheetsand graphene-graphite composites. Few-layer graphene (FLG) sheets can beproduced via various processes, including exfoliation of crystallinegraphite, epitaxial growth, chemical vapor deposition (CVD), thereduction of graphene oxide, and/or the like. Some of these processesare not suitable for large scale productions of FLG sheets. For example,micromechanical cleavage, colloquially known as the “Scotch Tape” methodwhere single and/or few-layer graphene sheets are exfoliated off ofgraphite by using adhesive tapes to peel off the sheets is usually anunpredictable process that tends to produce small flakes, and as such,at least for this reason doesn't lend itself for a large-scaleproduction of FLG sheets with large flake sizes and/or substantial flakesize to thickness form factors.

Processes such as epitaxial growth and CVD also suffer from severaldisadvantageous as scalable production methods of large flake sized FLGsheets. Both of these processes require vacuum settings for theproduction of FLG sheets, which increases the cost and complexity ofproduction and limits the applicability of these methods for large scalesynthesis of FLG sheets. In addition, both of these methods requirepost-production processing steps to remove the FLG sheets from thesubstrates used for growth or deposition, further undermining the appealof these methods for large scale FLG production for a variety ofpurposes (e.g., as additives in composites with polymers and ceramics).

Reduction of graphene oxide to obtain FLG sheets and/orgraphene-graphite composites also poses several problems that contributeto the unsuitability of graphene oxide reduction as a practical andscalable method for producing FLG sheets and/or graphene-graphitecomposites. For example, the quality of graphene obtained from suchprocesses is dependent on the quality of the precursor graphene oxideand the reducing agent, rendering the process unreliable andinconsistent, and usually producing graphene with poor crystallinequality and high in-plane defect density. Further, the reductionprocesses require the use of highly hazardous and unstable chemicalsthat increase the risks of toxic gas releases and other environmentallyunfriendly consequences. In light of at least these issues, grapheneoxide reduction processes do not commend themselves as methods of largescale production of FLG sheets and/or graphene-graphite composites oflarge flake sizes and/or substantial flake size to thickness formfactors.

Conventional methods that avoid using the above hazardous chemicalsinclude sonication of graphite in organic solvents to produce FLG sheetscan suffer other disadvantages. For example, such processes arenotoriously time consuming, making them unattractive as a method ofchoice for large scale FLG sheet production. Further, the yield rate isquite low, typically less than about 15% by weight, and additional,multi-step processes are required to exfoliate the remainingunexfoliated graphite. In addition, separating the exfoliated sheetsfrom the unexfoliated graphite is another tedious and time-consumingprocess. For at least these reasons, the aforementioned conventionalmethods prove themselves to be unsuitable as processes capable ofproducing large flake-sized thinned graphite in a scalable manner.

Production processes according to the embodiments described hereinovercome at least some of the disadvantages and shortcomings of theabove methods and processes for producing FLG sheets in a scalable andenvironmentally friendly manner. In some embodiments, the processes ofthe present disclosure include a two-step wet ball milling process whereone of the steps is largely mechanical and the other step is largelyelectrochemical. These processes, individually and/or in combination canbe configured to produce thinned graphite and/or graphite-graphenecomposites starting with a crystalline graphite precursor material. Thethinned graphite (e.g., single layer graphene, FLGs, etc.) and/orgraphite-graphene composites produced at least substantially accordingto the wet ball milling processes described herein have severalbeneficial properties, especially compared to the products of themethods and processes discussed above.

In some embodiments, the processes described herein can be configured toproduce thinned graphite and/or graphene-graphite composites thatsubstantially maintain the in-plane size of the precursor crystallinegraphite. For example, starting with graphite possessing substantialin-plane dimensions, in some embodiments, the disclosed wet-ball millingprocesses can produce graphene and/or thinned graphite that havesubstantially similar in-plane dimensions as the precursor material. Insome embodiments, the resulting thinned graphite may possess asubstantial flake size to thickness form factor, indicating that duringthe thinning of the precursor graphite by the wet-ball milling process,the in-plane dimensions of the precursor graphite have not been reducedsignificantly, as compared to some of the above processes such as theScotch Tape method where the flake sizes of the peeled off graphene orthinned graphite sheets are significantly smaller than the initialgraphite material.

The “efficiency” and/or effectiveness of producing thinned graphitewhile avoiding or minimizing reduction in lateral sheet size can becharacterized by a parameter such as an aspect ratio of the finalproduct of the process (e.g., thinned graphite, single layer graphene,FLG, etc.). The aspect ratio can be defined as a ratio of an in-planelateral dimension (also referred to herein as “lateral size”) to thethickness of the final product. For example, if a thinned crystallinegraphite final product has an average lateral dimension of 300 μm and athickness of 200 nm, the sheet size to thickness ratio, or “aspectratio”, can be defined as 300,000/200 (i.e., 1,500). As another example,if a FLG final product has an average lateral dimension of 1 μm and athickness of 1 nm (e.g., approximately three layers of graphene), theaspect ration can be defined as 1,000/1 (i.e., 1,000).

In some embodiments, the precursor graphite and/or the thinnedcrystalline graphite may not have a regular shape that allows for aconvenient identification of a measure of a lateral size, or even athickness. For example, as described herein, the precursor graphite canassume different forms, including rods, fibers, powders, flakes, and/orthe like. However, in some embodiments, depending on at least thegeometry of the precursor graphite/thinned graphite, generalizeddefinitions of thickness and/or lateral size can be used incharacterizing these quantities. In some embodiments, the thicknessand/or the in-plane lateral size of crystalline graphite in irregularforms can be characterized by a suitable linear dimension, and/oraverage of linear dimensions. For example, the thickness can be definedas some suitable length (e.g., height from topmost layer to bottom-mostlayer of a regularly layered graphite flake, average height ifirregularly shaped, etc.) in substantially the same direction as thedirection normal to the surfaces of the layered graphene sheets. Asanother example, the lateral size of crystalline graphite may be definedby some appropriate linear dimension and/or combination of dimensionsalong the surface of the graphite (e.g., diameter, average of severallinear dimensions along the surface, a linear dimension appropriatelynormalized by shape factors that take the geometrical irregularity ofthe graphite into consideration, etc.). In any case, suitable lineardimensions that characterize the thickness and the lateral size ofcrystalline graphite in an acceptable manner may be used in defining theaspect ratio as the ratio of the lateral size to the thickness.

In some embodiments, the wet ball milling processes described herein canbe configured to produce a final product with an aspect ratio muchhigher than values previously reported. For example, in someembodiments, the wet ball milling process can reduce the thickness of abulk precursor crystalline graphite to produce a thinned graphite havinga thickness of about 400 nm, or even lower, without a substantialreduction in the lateral sheet size of the precursor material (e.g., 500μm or higher). In such embodiments, in reducing the thickness of theprecursor graphite to down to 400 nm, the wet ball milling process canproduce a thinned graphite material having an aspect ratio of at leastabout 50, about 100, about 250, about 500, about 750, about 1,000, etc.,and all values and ranges therebetween. In some embodiments, a secondball milling process can be configured to produce a thinned graphitematerial and/or FLG sheets having an aspect ratio of at least about1,000, about 1,250, about 1,500, about 1,750, about 2,000, etc.,inclusive of all values and ranges therebetween. In some embodiments,these aspect ratios correspond to the reduction of crystalline graphitewith large lateral size to FLG sheets (including single layer) thatlargely maintain the substantial lateral size.

Further, the relative ease of at least some of the processes of thepresent disclosure in view of other processes such as epitaxial growthand CVD render these processes suitable for large scale production ofthinned graphite and/or graphene-graphite composites. As describedherein, processes such as epitaxial growth and CVD are expensive atleast for the reasons that they require a vacuum setting and costlypost-production processing steps at least as a result of the substratematerials that are needed during the growth/deposition processes.Moreover, as will be described in more detail below, in someembodiments, the precursor materials and the process conditions of theprocesses disclosed herein are inexpensive and not burdensome, incontrast to at least some of the processes described above.

In some embodiments, the wet ball milling processes of the presentdisclosure produces high-yield and/or high-quality thinned graphiteand/or graphite-graphene composites. For example, the processesdescribed herein can be configured to produce thinned graphite at ayield of grater than about 80%, about 85%, about 90%, about 95%, andeven in excess of about 99% purity by weight. In other words, theprocesses described herein can be configured to produce thinned graphiteat a yield that is significantly higher than the 15% yield rate of otherconventional methods. Such high yield rate carries the further advantagethat post-production processing steps to further thin the un-thinnedgraphite and/or otherwise purify the final product can be reduced orevent eliminated, thereby, reducing the cost and complexity that canarise from such steps.

In some embodiments, the wet ball milling processes described herein canbe configured to produce a graphene-graphite composite material. Informing a bond with graphite (e.g., thinned graphite), graphene has atendency to stack over the graphitic planes and become another layer inthe layered structure of graphite, thereby frustrating attempts toproduce graphene-graphite composites where the edges of the respectivegraphene and graphite are covalently bonded. The wet ball millingprocesses of the present disclosure can be configured to overcome thesedifficulties by, amongst other things, control and selectivefunctionalization of the edge structure of graphene so as to activatecovalent bonding and allow formation of graphene-graphite composites.

In some embodiments, a method for producing thinned crystallinegraphite, comprising the steps of transferring crystalline graphite intoa ball milling vessel, transferring a first solvent and a second solventinto the ball milling vessel, and rotating the ball milling vessel tocause shearing of layers of the crystalline graphite to produce thinnedcrystalline graphite is disclosed. In some embodiments, the crystallinegraphite includes at least one of natural graphite, synthetic graphite,highly oriented pyrolytic graphite (HOPG), graphite fiber, graphiterods, graphite minerals, graphite powder, and chemically modifiedgraphite. In some embodiments, the ball milling vessel includes agrinding media coated with an insulator, alumina, and/or zirconia. Insome embodiments, the grinding media and the crystalline graphite may beselected so that the mass ratio of the grinding media to the crystallinegraphite is in a range of about 1:1 to about 60:1, about 5:1 to about30:1, etc. In some embodiments, the ball milling vessel includes atleast one of an attritor ball mill, a planetary ball mill and a shearmixer, and further comprises a semiconductor and/or an insulatormaterial.

In some embodiments, the first solvent can be different than the secondsolvent, and may have a first surface tension different than a secondsurface tension of the second solvent, wherein the difference betweenthe first surface tension and the second surface tension is configuredto facilitate the shearing of layers of the crystalline graphite. Forexample, the first surface tension can be in the range of about 10 mN/mto about 50 mN/m, and the second surface tension can be in the rangefrom about 50 mN/m to about 100 mN/m, and in some embodiments, both thefirst surface tension and the second surface tension can be in the rangeof about 10 mN/m to about 50 mN/m. In some embodiments, the differencebetween the first surface tension and the second surface tension can bein the range of about 0 N/m to about 75 mN/m, or about 40 mN/m to about60 mN/m, etc. Further, the first solvent and the second solvent can beconfigured to trap at least a portion of the crystalline graphitebetween the first solvent and the second solvent. For example, the firstsolvent can have a first density and the second solvent can have asecond density different than the first density, the difference betweenthe first density and the second density can be configured to facilitatethe trapping of the at least a portion of the crystalline graphitebetween the first solvent and the second solvent. For example, the firstdensity can be in the range of about 500 kg/m³ to about 850 kg/m³, andthe second density can be in the range of about 850 kg/m³ to about 1,200kg/m³. In some embodiments, both the first density and the seconddensity can be in the range of about 650 kg/m³ to about 850 kg/m³, andyet in some embodiments, the difference between the first density andthe second density can be in the range of about 0 kg/m³ to about 1,200kg/m³.

In some embodiments, the first solvent and the second solvent caninclude any two of water, heptane, ethanol, and acetonitrile. Forexample, the first solvent can be water and the second solvent can beheptane, and they can be used in the wet ball milling process in thevolumetric ratio in the range of about 1:20 to about 1:1, in the rangeof about 1:10 to about 1:5, etc. As another example, the first solventcan be ethanol and the second solvent can be acetonitrile.

In some embodiments, the product of the wet ball milling process, thethinned crystalline graphite can have a thickness in the range of about1 graphene layer to about 1,200 graphene layers, about 1 graphene layerto about 100 graphene layers, about 1 graphene layer to about 10graphene layers, about 1 graphene layer to about 3 graphene layers, etc.In some embodiments, the thinned crystalline graphite can have athickness of less than about 400 nm, less than about 300 nm, less thanabout 200 nm, less than about 100 nm, less than about 50 nm, less thanabout 20 nm, less than about 10 nm, less than about 5 nm, less thanabout 1 nm, etc. In some embodiments, the thinned crystalline graphiteand/or the precursor crystalline graphite can have a lateral dimensionof in a range of about 10 nm to about 500 μm. For example, an averagelateral dimension of the crystalline graphite can range at least up toabout 800 μm, at least up to about 500 μm, at least up to about 200 μm,etc. In some embodiments, the average lateral dimension can be in arange from about 200 nm to about 20 μm, from about 200 nm to about 500nm, from about 500 nm to about 5 μm, from about 5 μm to about 20 μm,etc. In some embodiments, when the average lateral size is in the rangefrom about 5 μm to about 20 μm, the thickness of the crystallinegraphite can be about 3 to 4 graphene layers (equivalently about 0.9 nmto about 1.2 nm), corresponding to an aspect ratio ranging from about 5μm/1.2 nm (i.e., — 4,000) to about 20 μm/0.9 nm (i.e., — 22,000). Insome embodiments, when the average lateral size is in the range fromabout 0.5 μm to about 5 μm, the thickness of the crystalline graphitecan be about 2 to 3 graphene layers (equivalently about 0.3 nm to about0.6 nm), corresponding to an aspect ratio ranging from about 0.5 μm/0.6nm (i.e., — 830) to about 5/0.3 nm (i.e., 1,500). And yet in someembodiments, when the average lateral size is in the range from about0.2 μm to about 0.5 μm, the thickness of the crystalline graphite can beabout 1 to 2 graphene layers (equivalently from single atom layer toabout 0.3 nm graphene interlayer spacing), corresponding to an aspectratio of about 1,000.

In some embodiments, the wet ball milling process includes rotating theball milling jar or vessel at a desired speed for a given duration oftime. For example, to produce the thinned crystalline graphite, in someembodiments, the ball milling vessel is rotated for about 2 hours toabout 100 hours, for about 3 hours to about 48 hours, for about 3 hoursto about 24 hours, etc. The speeds the milling vessel is rotated at canalso range from about 10 rpm to about 225 rpm, from about 10 rpm toabout 150 rpm, from about 25 rpm to about 75 rpm, and/or the like.

In some embodiments, the method for producing thinned crystallinegraphite can include a second wet ball milling process. The process caninclude isolation of the thinned crystalline graphite from the firstsolvent and the second solvent, either by draining the first solvent andthe second solvent from the ball milling vessel, and/or transferring thethinned crystalline graphite to a second ball milling vessel. In someembodiments, the method includes the addition of additional solventsand/or additives into the ball milling vessel containing the thinnedcrystalline graphite. For example, the method can include transferring ametal hydroxide salt into the second ball milling vessel, transferring athird solvent into the second ball milling vessel, transferring anoxidizer into the second ball milling vessel, and rotating the secondball milling vessel to generate an electrostatic charge, wherein oxygenreleased from a hydroxyl ion that is ionized by the generatedelectrostatic charge intercalates the thinned crystalline graphite toexfoliate layers of the thinned crystalline graphite. In someembodiments, the metal hydroxide salt can be formulated to release ahydroxyl ion upon ionization by the electrostatic charge, and mayinclude at least one of alkali metals, alkaline earth metals, andelements of the boron group. In some embodiments, the third solvent canbe formulated to facilitate diffusion of the hydroxyl ion and/orproduction of the electrostatic charge in the second ball millingvessel. Examples of the third solvent include includes at least one ofN,N-Dimethylformamide, chlorobenzene, dimethyl sulfoxide,N-methyl-2-pyrrolidinone, 1-propanol, and mixtures thereof.

In some embodiments, the method may further include the step oftransferring a fourth solvent into the second ball milling vessel,wherein the forth solvent has a fourth surface tension different fromthe third surface tension of the third solvent. In some embodiments, thedifference between the third surface tension and the fourth surfacetension can be configured to facilitate the shearing of the layers ofthe thinned crystalline graphite. In some embodiments, the volumetricratio of the fourth solvent to the third solvent is in a range of about1:50 to about 1:1, in a range of about 1:20 to about 1:5, and/or thelike.

In some embodiments, the oxidizer can be formulated to interact with thehydroxyl ion to release oxygen that may be at least partiallyresponsible for the exfoliation of the thinned graphite. In someembodiments, the oxidizer, an example of which includes hydrogenperoxide, may comprise less than about 3 percent, about 1%, etc., of thecontents of the second ball milling vessel.

In some embodiments, the method of producing thinned crystallinegraphite may include the process of ball milling the contents of thesecond ball milling vessel by rotating the vessel at some desired speedfor a given duration of time. For example, to exfoliate the layers ofthe thinned crystalline graphite, in some embodiments, the second ballmilling vessel may be rotated for a time duration ranging from about 2hours to about 100 hours, from about 2 hours to about 10 hours, fromabout 1 hour to about 6 hours, etc. The speed of rotation may include,in some embodiments, a speed ranging from about 10 rpm to about 250 rpm,from about 150 rpm to about 225 rpm, from about 10 rpm to about 75 rpm,etc.

In some embodiments, surfactants can be used for, amongst other things,to avoid the agglomeration of the contents of the second ball millingvessel. Accordingly, in some embodiments, the method may further includethe step of transferring a surfactant into the second ball millingvessel, the surfactant formulated to increase the conductivity of thecontents of the second ball milling vessel. In some embodiments, theconcentration of the surfactants to be included may vary from about 10μMolar to about 100 μMolar, from about 10 μMolar to about 50 μMolar,etc. Examples of the surfactants include at least one of sodium dodecylsulfate (SD S), pyridinium (PY+), thionin acetate salt, and triton.

In some embodiments, the resulting thinned graphite can be mixed withother materials to, for example, produce composites suited for variouspurposes. For example, the exfoliated graphite can be mixed with a metalto produce a metal-thinned graphite composite with enhanced thermalconductivity. Examples of such metals include but are not limited totitanium, copper, and silicon. In some embodiments, the materials can beoxides such as titanium oxide and titanium dioxide, and the resultingoxide-thinned graphite composite may possess improved thermal and/orelectrical conductivities. Such enhanced thermal and/or electricalconductivities allow for the composite materials to be used in variousapplications, including cooling systems, electrical systems, etc.

As used herein, the term “crystalline graphite” or “precursorcrystalline graphite” refers to graphite based material of a crystallinestructure with a size configured to allow ball milling in a ball millingjar. For example, the crystalline graphite can be layered graphenesheets with or without defects, such defects comprising vacancies,interstitials, line defects, etc. The crystalline graphite may come indiverse forms, such as but not limited to ordered graphite includingnatural crystalline graphite, pyrolytic graphite (e.g., highly orderedpyrolytic graphite (HOPG)), graphite fiber, graphite rods, graphiteminerals, graphite powder, flake graphite, any graphitic materialmodified physically and/or chemically to be crystalline, and/or thelike. As another example, the crystalline graphite can be graphiteoxide.

As used herein, the term “thinned graphite” refers to crystallinegraphite that has had its thickness reduced to a thickness from about asingle layer of graphene to about 1,200 layers, which is roughlyequivalent to about 400 nm. As such, single layer graphene sheets,few-layer graphene (FLG) sheets, and in general multi-layer graphenesheets with a number of layers about equal to or less than 1,200graphene layers can be referred as thinned graphite.

As used herein, the term “few-layer graphene” (FLG) refers tocrystalline graphite that has a thickness from about 1 graphene layer toabout 10 graphene layers.

As used herein, the term “lateral size” or “lateral sheet size” relatesto the in-plane linear dimension of a crystalline material. For example,the linear dimension can be a radius, diameters, width, length,diagonal, etc., if the in-plane shape of the material can be at leastapproximated as a regular geometrical object (e.g., circle, square,etc.). If the in-plane shape of the material can not be modeled byregular geometrical objects relatively accurately, the linear dimensioncan be expressed by characteristic parameters as is known in the art(e.g., by using shape or form factors).

As used herein, the term “grinding media” or “milling balls” refer toany grinder that can be used in the exfoliation and thinning ofcrystalline graphite in ball milling jars. Even though the commonnomenclature “milling balls” is used, the grinding media or the millingballs are not limited to a particular geometry, and can have any desiredproperty such as shape, size, composition, etc.

In some embodiments, with reference to FIG. 1 , crystalline graphite,one or more solvents, and a grinding media can be added into a ballmilling vessel to commence a wet ball milling process for a large scaleproduction of thinned graphite and/or graphene-graphite composites,e.g., step 101. In some embodiments, an oxidizer can also be included inthe ball milling vessel. In some embodiments, the wet ball millingprocess can be a two-step or two stage wet ball milling process. In someembodiments, the crystalline graphite comprises ordered graphiteincluding natural crystalline graphite, pyrolytic graphite (e.g., highlyordered pyrolytic graphite (HOPG)), graphite fiber, graphite rods,graphite minerals, graphite powder, flake graphite, any graphiticmaterial modified physically and/or chemically to be crystalline, and/orthe like. The lateral or in-plane size of the ordered graphite canassume a wide range of values. For example, using an appropriate measureto quantify the lateral size of the ordered graphite (e.g., mean lateralsizes, diameter, etc., depending on the shape, for example), the lateralsheet size of the ordered graphite can range from about 10 nm to about500 μm. Some embodiments of the graphite thinning processes disclosedherein can be configured to produce thinned graphite that substantiallypreserves the large lateral sizes of the precursor crystalline graphite.As such, in some embodiments, the resulting thinned graphite can have alateral sheet size in the range of from about 10 nm to about 500 μm.

In some embodiments, any solvents capable of aiding in the exfoliationof the layers of the ordered crystalline graphite can be used in theprocesses disclosed herein. In some embodiments, the volume of totalsolvent content to be used in the processes can depend on the amount ofthe precursor crystalline graphite. However, the proportion of a firstsolvent to a second solvent can be designed to allow maximal contact ofthe solvents to crystalline graphite surface area so as to allowenhanced shearing of layers of the crystalline graphite as a result ofdensity and/or surface tension differentials of the solvents. Forexample, the solvents can include two solvents that have differentsurface tensions, and can also be immiscible or semi-miscible solventsincapable of making a homogenous mixture when combined. Said anotherway, the solvents chosen may have properties configured to trap thecrystalline graphite between the solvents (e.g. at their interface). Inaddition, the crystalline graphite can be exposed to a surface tensiondifferential shear force that contributes to the shearing of the layers,and hence the thinning of the graphite material during wet ball millingprocesses. In some embodiments, at least one of the one or more solventscan be configured to penetrate between layers of the ordered graphiteand weaken the forces (e.g., van der Waals force) that hold the layerstogether, thereby contributing to the thinning of the graphite duringthe ball milling processes.

In some embodiments, the one or more immiscible or semi-misciblesolvents can be selected so as to possess large differences in theirrespective densities and/or surface tensions. In most cases, largedifferences in densities lead to the formation of separate layers ofsolvents with the lighter solvent (i.e., the solvent with lower density)residing above the denser solvent. In some instances, this facilitatesthe trapping of the graphite material in between the layers of the twosolvents. As an example, one of the two solvents can have a densityranging from about 400 kg/m³ to about 800 kg/m³ and the other can have adensity ranging from about 800 kg/m³ to about 1,200 kg/m³, and thedifferences in their densities allows them to trap crystalline graphitein between them. Thus, the difference in densities of the two solventscan be in the range of about 0 kg/m³ to about 800 kg/m³, from about 100kg/m³ to about 700 kg/m³, from about 200 kg/m³ to about 600 kg/m³, fromabout 300 kg/m³ to about 500 kg/m³, from about 350 kg/m³ to about 450kg/m³, and/or the like. And as discussed above, when the two immiscibleor semi-miscible solvents have large differences in surface tensions, insome embodiments, the differences give rise to a shearing force thatexfoliates the layers of the trapped crystalline graphite. As anexample, one of the two solvents can have a surface tension ranging fromabout 15 mN/m to about 50 mN/m, and the other of the two solvents canhave surface tension ranging from about 50 mN/m to about 100 mN/m. Thus,the difference in surface tension of the two solvents can be in therange of about 0 mN/m to about 85 mN/m, from about 10 mN/m to about 75mN/m, from about 20 mN/m to about 65 mN/m, from about 30 mN/m to about60 mN/m, from about 40 mN/m to about 60 mN/m, or from about 45 mN/m toabout 55 mN/m.

One example of two immiscible solvents that can be used in the thinningof graphite is water and heptane (C₇H₁₆). Under normal conditions (e.g.,standard temperature and pressure), heptane has a density of about 680kg/m³ and water has a density of about 1,000 kg/m³. As immisciblesolvents, heptane and water do not mix, and the density differential canresult in layers of heptane forming above water, creating an interfacefor trapping crystalline graphite to be sheared and thinned. Further,under some conditions (e.g., at temperature about 20°), heptane has asurface tension of about 20 mN/m, while water's is a relatively highsurface tension of about 73 mN/m, and such large differential cancontribute to the shearing of layers off of the ordered crystallinegraphite during the wet ball milling process. In some embodiments, theproportional amounts of water and heptane that can be included in theseprocesses can be quite varied. For example, in some embodiments, waterand heptane can be included in the first step of the ball millingprocess in a 1:20 proportion. In some embodiments, the proportions canbe about 1:18, about 1:16, about 1:14, about 1:12, about 1:10, about1:8, about 1:6, about 1:4, about 1:2 or about 1:1, inclusive of allranges and values therebetween. In other words, the proportions can bein a range from about 1:20 to about 1:1. For example, the water toheptane proportion can be in the range from about 1:18 to about 1:2,from about 1:16 to about 1:4, from about 1:14 to about 1:6, from about1:12 to about 1:8, etc. In some embodiments, a lower proportion ofheptane (e.g., lower than 1:1) can be used, but complications may arisedue to issues related to disposal of heptane after usage.

In some embodiments, one or more solvents whose differences inrespective densities and/or surface tensions are relatively small canalso be used for thinning graphite in wet ball milling processes. Forexample, a pair of semi-miscible solvents, ethanol and acetonitrile,have comparable densities and surface tensions, i.e., the differencesare relatively small. For example, under some conditions (e.g., attemperature about 20°), ethanol has a density of about 780 kg/m³ andacetonitrile has a density of about 786 kg/m³. In addition, ethanol hasa surface tension of about 22 mN/m while acetonitrile has a surfacetension of about 19 mN/m. Although ethanol and acetonitrile aresemi-miscible and the differences in densities and surface tension arenot as high (e.g., compared to water and heptane), in some embodiments,these two solvents are capable of facilitating the thinning of graphiteduring wet ball milling. In some embodiments, the proportional amountsof ethanol and acetonitrile that can be included in these processes canbe quite varied. For example, the volume proportion of ethanol toacetonitrile can range from about 5:1 to about 1:10. In someembodiments, the volume proportion can range from about 4:1 to about1:8, from about 3:1 to about 1:6, from about 2:1 to about 1:4, fromabout 1:1 to about 1:3, etc. In some embodiments, the volume proportioncan range from about 5:1 to about 5:3, from about 5:3 to about 1:1, fromabout 1:1 to about 1:3, from about 1:3 to about 1:7, from about 1:7 toabout 1:10, etc.

It is to be noted that the above pairs of solvents are exemplary, andother combinations of solvents can be used during the wet ball millingprocess. In some embodiments, any solvents with sufficient densityand/or surface tension differentials can be used during the wet ballmilling process. Examples of suitable solvents include, but are notlimited to water, ethanol, heptane, acetonitrile, N,N-Dimethylformamide,chlorobenzene, dimethyl sulfoxide, N-methyl-2-pyrrolidinone, 1-propanol,and/or the like can be used as the solvents in the wet ball millingprocesses.

In some embodiments, the crystalline graphite, the one or more solvents,the oxidizer and a grinding media can be placed into a jar to commencethe ball milling process. In some embodiments, the ball milling processcan be carried out in any type of grinding mill system that comprises amill jar and allows for the shearing and exfoliation of the crystallinegraphite into thinned graphite and/or graphene-graphite compositematerials. Examples of grinding mill system that can be used for theball milling process include mills such as but not limited to ballmills, rod mills, pebble mills, autogenous mills, semi-autogenous mills,roller mills (e.g., jar roller mills, ring mills, frictional-ball mills,etc.), attritors, planetary mills, jet mills, aerodynamic mills, shearmixers, and/or the like. In some embodiments, the mill jars can be madefrom insulators and/or semi-conductors, including ceramic materials,alumina, stainless steel, and/or zirconia, and can also be lined withmaterials such as polyurethane, rubber, etc. In some embodiments, themills include grinding media for aiding in the grinding/shearing ofprecursor materials such as graphite. In some embodiments, the grindingmedia can be made from the same type of materials as the mill jar inwhich the grinding media are being used in. For example, the grindingmedia can be made from alumina, zirconia, etc. In some embodiments, thegrinding media may assume different forms. For example, the grindingmedia can be at least substantially a ball (hence the term “ballmilling”), at least substantially a cylinder, at least substantially arod, and in fact any shape capable of aiding the grinding/shearing ofprecursor materials. Example schematics of the ball milling of a ballmilling vessel or jar comprising graphite, milling balls, and a solutionis shown in FIGS. 2A and 2B.

At step 102, in some embodiments, the mix comprising crystallinegraphite, a first solvent, a second solvent and an oxidizer are ballmilled by rotating the ball mill containing the mix and milling balls ata relatively low rotational speed. The crystalline graphite can be ofany size that can reasonably fit into the mill jar and allow the wetball milling process to proceed without undue interference by anoperator. For example, in some embodiments, the precursor crystallinegraphite can have a lateral size of up to about 500 μm. However, in someembodiments, the ball milling process can be carried out efficientlywhen the grinding media (e.g., the milling balls) are proportional tothe crystalline graphite. The proportionality can be in weight, size,volume, density, etc.

In some embodiments, the number of milling balls in the milling jar candepend on milling process related factors such as but not limited to therunning time, the rotational speed, amount/size of the crystallinegraphite, size of the milling balls (e.g., average size), and/or thelike. For example, for a given amount of crystalline graphite, there canbe some milling ball sizes (conversely number of milling balls) that canbe particularly beneficial in effecting a more efficient shearing ofcrystalline graphite layers depending on the speed and the length of theball milling process. For example, at a rotation speed of about 50 rpmand a running time of about 50 hours, the average size of a milling ballin the milling jar can be about 5 mm.

In some embodiments, the precursor crystalline graphite can have a widerange of quality measures with respect to parameters such as defectpresence/density (missing particles, displacements, etc.), presenceand/or density of extraneous particles, and/or the like. In someembodiments, the precursor material can have pure graphite in the rangeof from about 40% to about 100% by weight. In some embodiments, theweight percentage of pure graphite in the precursor material can be in arange of from about 50% to about 90%, from about 60% to about 80%, fromabout 40% to about 60%, from about 60% to about 80%, from about 80% toabout 100%. For example, the precursor can have graphite content ofabout 95% by weight according to some embodiments. In some embodiments,after the wet balling milling process produces thinned graphite and theresulting thinned graphite is washed as described later, the purity ofthe resulting graphite can be about 99% by weight.

In some embodiments, the mixture may comprise an oxidizing agent in asmall amount by volume. For example, the mixture may comprise anoxidizer in the amount of about 1 percent or less by volume, about 3percent or less by volume, etc. Examples of oxidizing agents includehydrogen peroxide, perchloric acid, nitric acid, and/or the like.

In some embodiments, the speed of the rotation is configured to reducethe initial thickness of graphite material without substantiallyaffecting its lateral size. For example, the stronger mechanicalinteraction between the milling balls and the crystalline graphite thatcould result as a result of higher ball milling rotational speed canreduce not only the thickness of the crystalline graphite, but also itslateral size. In some embodiments, the ball milling speed can range fromabout 10 rotations per minute (rpm) to about 500 rpm. In someembodiments, the ball milling speed can range from about 10 rpm to about250 rpm, about 10 rpm to about 225 rpm, about 10 rpm to about 150 rpm,about 10 rpm to about 100 rpm, about 25 rpm to about 75 rpm, from about50 rpm to about 300 rpm, from about 150 rpm to about 250 rpm, and/or thelike. In some embodiments, the ball mill may be rotated at a relativelylow ball milling rotational speed of about 50 rpm. In some embodimentswhere the ball mill is rotated at a low speed, it can take several hoursbefore the crystalline graphite is thinned to hundreds of layers. Insome embodiments, the ball milling rotation to reduce the thickness ofthe crystalline graphite (starting from “bulk” thickness of, forexample, several micron thickness) to about 400 nm may take from about 2hours to about 100 hours. In some embodiments, the process can take fromabout 2 hours to about 48 hours, about 3 hours to about 24 hours, about6 hours to about 12 hours, and/or the like. For example, rotating atabout 50 rpm, it may take about 50 hours to reduce the thickness of aprecursor crystalline graphite to about 200 nm thickness.

In some embodiments, the first step of the wet ball milling process mayreduce the precursor crystalline graphite to a thickness much less thanabout 400 nm, for example, about 200 nm. However, such embodiments areusually accompanied with reduction in lateral size of the crystallinegraphite, and as such may be avoided when the goal is to obtain thinnedgraphite that maintain the sheet size of the precursor crystallinegraphite.

At step 103, in some embodiments, the thinned crystalline graphite canbe isolated from the other ingredients used after the first step of thewet ball milling process. For example, the solvents and the oxidizer canbe drained out of the ball milling jar, leaving behind at least thethinned graphite. In some embodiments, the isolation can take place bytransferring some or all of the thinned graphite to another ball millingjar. In such embodiments, the ball milling jar and the grinding media tobe included in the jar can be the same, substantially similar ordifferent than those used in the first step of the wet ball millingprocess. An example end product of the wet ball-milling process asdisclosed herein is shown in FIG. 3 . The figure shows an atomic forcemicroscopy image of a thinned graphite of about 35 graphene layersproduced as a result of the first step of the ball milling process.

At step 104, in some embodiments, one or more solvents for the secondstep of the wet ball milling process can be added into the milling jar.In some embodiments, the criteria for selecting the solvent can includethe same or similar conditions used to select the solvents for the firststep of the wet ball milling process. For example, the solvents can havedifferent density and/or surface tension values so as to trap thethinned graphite in between the solvents and aid with the furthershearing of the thinned graphite. In addition, at least one of the oneor more solvents can be capable of penetrating between layers of thethinned graphite, contributing to the weakening of the interlayer vander Waals bonds and the intercalation and exfoliation of graphite. Insome embodiments, the one or more solvents can comprise an organicsolvent configured to facilitate the production of electrostatic chargesduring the wet ball milling of the thinned graphite, which contribute tothe exfoliation of the already thinned graphite as will be discussedbelow.

In some embodiments, the one or more solvents for use during the secondstep of the wet ball milling process can comprise a non-polar solventsuch as water and a polar solvent such as the organic solventacetonitrile. It is to be noted that the above pairs of solvents areexemplary, and other combinations of solvents can be used during the wetball milling process. For example, a selection of a polar solvent and anon-polar solvent from the list comprising water, heptane,N,N-Dimethylformamide, acetonitrile, ethanol, chlorobenzene, dimethylsulfoxide, N-methyl-2-pyrrolidinone, 1-propanol, and/or the like can beused as the solvents for use in the second step of the wet ball millingprocess.

In some embodiments, a metal hydroxide salt configured to interact withelectrostatic charges to produce metal and hydroxide ions can be addedinto the milling jar of the second step of the wet ball milling process.For example, a metal hydroxide such as KOH may interact with theelectrostatic charges produced during the wet ball milling process andrelease a hydroxyl (OH⁻) ion which, as will be discussed below cancontribute to the production of oxygen atoms that intercalate graphiteand lead to exfoliation of graphitic layers. Metal hydroxides comprisingmetals selected from alkali metals, alkaline earth metals, boron groupelements, etc., and hydroxyl ion can be used for such processes. Forexample, hydroxides of Li, Na, K, Cs, Be, Mg, Ca, Sr, Ba, B, Al, Ga, In,and Ti, and mixtures thereof, can be used as metal hydroxide saltsduring the second step of the wet ball milling process. In someembodiments, the amount of metal hydroxide salt to be used in the wetball milling process can assume a wide range of values. For example,considering the solution comprising the solvents and the hydroxide salt,the hydroxide salt can be from about 2% to about 50% of the solution byvolume. In some embodiments, for high yield production (e.g., greaterthan about 60% of the treated precursor graphite powder reduces to FLG,i.e., to about a thinned graphite of 10 layers or less), metalshydroxides comprising alkali and/or alkaline earth metals can be used,while for low yield production, metals hydroxides comprising metals fromboron group elements can be used. In some embodiments, in particular forthe purpose of doping resulting graphene sheets with metal particles,the amount of metal hydroxide can be increased to about 90% of thesolution by volume.

In some embodiments, an oxidizing agent (i.e., oxidizer) can be used inthe second step of the ball milling process to, amongst other things,interact with hydroxyl ions to generate atomic oxygen that canintercalate graphite and weaken the interlayer van der Waals bonds. Insome embodiments, the oxidizer is also configured to oxidize edges ofgraphite, paving the way for the formation of graphene-graphitecomposites. An example of such an oxidizer is hydrogen peroxide (H₂O₂).In some embodiments, the oxidizer can be used in a small amount. Forexample, the mixture in the milling jar comprising the one or moresolvents, the thinned graphite, the metal hydroxide salt, and othercomponents such as surfactants and the like may comprise hydrogenperoxide in the amount of about 1 percent or less by volume. In someembodiments, the amount of hydrogen peroxide may be about 3 percent byvolume or less.

In some embodiments, surfactants can be included in the wet ball millingprocess to avoid or minimize clamping of the end products of the ballmilling process. Surfactants increase the conductivity of the mixture inthe milling jar, allowing for an increased diffusion of the hydroxylions and thereby contributing to the exfoliation of layers of thecrystalline graphite. Further, surfactants enhance the shearing forceimparted on crystalline graphite (e.g. precursor or thinned) as a resultof the incongruity of the surface tensions of the one or more solventsused during ball milling processes. The enhancement in the shearingforce further contributes to the further thinning of the thinnedcrystalline graphite by, for example, exfoliation. Examples ofsurfactants that can be used during wet ball milling processes (e.g.,the second step and/or the first step) comprise sodium dodecyl sulfate(SDS), pyridinium (PY+), thionin acetate salt, triton, etc., andmixtures thereof.

In some embodiments, the concentration of surfactants to be used duringthe wet ball milling processes can be determined based on the desire tomaintain balance between the thinning and the reduction in lateral sizeof the crystalline graphite. As discussed above, in some embodiments,surfactants enhance the shearing force on crystalline graphite andfacilitate the thinning of the crystalline graphite. On the other hand,a large amount of surfactants (e.g., more than the amount used to avoidor minimize agglomeration of crystalline graphite) can lead to reductionin lateral size, which may be undesirable in some circumstances.Accordingly, in some embodiments, an average concentration of betweenabout 10 μMolar and about 100 μMolar of surfactants can be used duringwet ball milling process to thin crystalline graphite into thinnedand/or single or few layers of graphene sheets.

At step 105, in some embodiments, a mixture comprising the thinnedgraphite, solvents (e.g., polar and non-polar), the metal hydroxidesalt, the oxidizer, and surfactants is ball milled in the milling jarfor a large scale synthesis of thinned graphite and/or graphene-graphitecomposites. Depending on the goal for the end product of the wet ballmilling process (e.g., thinned graphite, thinned graphene-graphitecomposite, final thickness, final purity, etc.), in some embodiments,the rotation speed and/or the milling period can be adjusted. Forexample, to further thin the thinned graphite, the milling jar may berotated at a relatively low speed for an extended period of time in amanner similar to the first step of the wet ball milling process. Forexample, the ball milling can be performed at a speed of about or lowerthan about 50 rpm for a period ranging from about 2 hours to about 100hours, from about 3 hours to about 50 hours, from about 3 hours to about24 hours, etc.

In some embodiments, the goal for the wet ball milling process may be toobtain thinned graphene-graphite composite, and in such embodiments, thespeed of rotation can be raised to higher ranges. For example, the speedof rotation can be increased to the range from about 50 rpm to about 225rpm, from about 100 rpm to about 200 rpm, from about 150 rpm to about175 rpm, etc. Further, the rotation time length can be decreased to ashorter period. For example, the period of rotation can be in the rangeof from about 1 hour to about 6 hours. In some instances, the period maybe in the range of from about 2 hours to about 4 hours.

In some embodiments, the ball milling of the aforementioned mixturegenerates electrostatic charge that contributes to the exfoliation oflayers from the crystalline graphite (already thinned or otherwise). Forexample, the generated electrostatic charge can initially appear on thesurface of the milling balls and/or on the inner parts of the millingjars. In some embodiments, the electrostatic charge remains localizeduntil the conductivity of the mixture attains a threshold that allowsthe charge to diffuse through the mixture. The conductivity of themixture can be affected by several factors including the presence andconcentration of the organic solvent. During the process, in someembodiments, the electrostatic charge can transfer through the liquidand ionize the metal hydroxide salt to produce metal cations andhydroxide anions (i.e., hydroxyl). In some embodiments, the productionof hydroxide anions can be improved by increasing the milling/rotationspeed as higher rotation speed enhances localized electrostatic chargesand lead to increases in the concentration of hydroxide anions. However,the increased speed also contributes to reduction in lateral sheet sizeof the crystalline graphite. For example, increasing the ball millingrotational speed can result into stronger mechanical interaction betweenthe milling balls and the crystalline graphite, resulting in thereduction of graphitic lateral sheet size (and graphene/thinned graphitesheet size). In such embodiments, the speed of rotation can bedetermined with a view towards balancing the competing needs forenhanced production of hydroxide anions and the ensuing reduction inlateral sheet size. An example schematics of the ball milling of a ballmilling vessel or jar producing electrostatic charges is shown in FIG.2B.

In some embodiments, upon production of the hydroxide anions during thesecond step of the wet ball milling process, the anions can diffusethrough the mixture and attack edges of the crystalline graphite layers,delaminating the edges and opening paths for the organic solvent toaccess the inter-atomic spaces between the layers. In some embodiments,the entering of the organic solvent into the interlayer spacing leads tothe weakening of the van der Waals bonds between the graphite layers,and facilitates the shearing of the layers of the crystalline graphite.Further, the hydroxyl ions can interact with the water solvent and/orthe oxidizer (e.g., hydrogen peroxide) to produce atomic oxygen that canserve as an exfoliating agent. For example, the oxygen can intercalategraphite and expand the interlayer separation, thereby weakening the vander Waals bonds in between the graphene layers. Once the shearing forcefrom the wet ball milling process exceeds the van der Waals force, insome embodiments, exfoliation of layers of graphene takes places,resulting in the thinning of the crystalline graphite and/or productionof graphene layers. For example, the exfoliation process describedherein can further reduce the thickness of a thinned graphite (e.g., alarge lateral-sized (e.g., about 500 μm) crystalline graphite thinned toabout 400 nm during the first step of the wet ball milling process) fromabout 400 nm thinness to a thickness in the range from about 200 nm toabout 400 nm. In some embodiments, such reduction in thickness can beobtained without a substantial reduction in lateral (in-plane) size ofthe thinned graphite, depending on factors such as the rotation speed ofthe milling process, etc., resulting in an increase in the aspect ratioindicating an efficient process and a high quality product. In someembodiments, further ball milling can reduce the thickness of thegraphite to an even lower thickness of few layers of graphene. Forexample, the thickness can decrease to the range of about 1 nm to about5 nm (corresponding to from about 3 layers of graphene to about 15layers). However, in some embodiments, such a process may also reducethe lateral size of the thinned graphite to about several microns (forexample, down from about 500 μm lateral size). In some embodiments, thegraphite thickness can be further reduced to even fewer layers of asingle or two layers of graphene (e.g., less than about 1 nm). In someembodiments, the lateral seize can decrease to about 300 nm. In someembodiments, the aspect ratio may not change as much, or even increase,indicating that the reduction in thickness may have been obtained at thecost of reduced flake size.

In some embodiments, the diffusion process of the anions can beproportional to the density of the electrostatic charges in the millingjar and correlate with the ionization voltage and production yield ofexfoliated graphene or thinned graphite. Further, diffusion length ofhydroxide anions can be dependent upon organic solvent concentration,presence and/or concentration of an oxidizer, quality and/or purity ofthe precursor crystalline graphite, etc.

Exfoliation of crystalline graphite with the aid of electrostaticcharges is advantageous in that large quantities of large grapheneand/or thinned graphite sheets can be produced at a relatively quickpace using an environmentally friendly process that does not used strongacids and/or release noxious gases. In some embodiments, the wet ballmilling process of the present disclosure may be carried out attemperatures that avoid the loss of solvents in the mixture (e.g.,water). For example, the process can take place at room temperature.Further, in some embodiments, the resulting graphitic product containslittle or no defects (because of absence of strong acids and/or largemechanical forces, for example), and can be highly dispersive duringapplications as a result of the functionalized edge structures. Forexample, hydroxylated graphene can have better dispersibility in aqueoussolutions and could be more amenable to mixing with metals and/or metaloxides.

In some embodiments, the resulting graphene and/or thinned graphite canbe edge functionalized with the hydroxyl ions which facilitate thedispersion of graphene and/or thinned graphite in metals, ceramics, somepolymers, etc., during applications. For example, further milling and/orlow concentration of the oxidizer can result in saturated electrostaticcharges accumulating on the surface of graphite particles and on theedges of graphene, and such charges allow for the functionalization ofgraphene and/or thinned graphite edges by bonding with hydroxyl ionsand/or process by products such as but not limited to hydrogen atoms.The functionalization of graphene and/or thinned graphite has severaluseful properties. For example, in some embodiments, the appearance ofhydroxyl ions on the edge of graphene and/or thinned graphite canincrease the thermal stability of the processed product. In someembodiments, the formation of graphite-graphene composites follows fromthe activation or functionalization of the edges as activated edges havea large tendency to covalently bond with the surface of graphiteparticles, resulting in the formation of graphite-graphene composites inwhich graphene is bonded covalently with graphite rather than via vander Waals bonds. FIGS. 4A and 4B show an example scanning electronmicroscopy image of graphene-graphite composite produced as a result ofthe second step of the ball milling process.

In some embodiments, the appearance of hydroxyl ions on the edge ofgraphene and/or thinned graphite can increase the thermal stability ofthe processed product. For example, FIG. 5 shows results of athermogravimetric analysis profiling the thermal stability of commercialgraphene 501, exfoliated graphene 502 and thinned graphite 503 (thinnedaccording to the processes disclosed herein). Compared to commercialgraphene, FIG. 5 shows that thinned graphite 503 of the presentdisclosure has a higher thermal stability and hence decomposes at ahigher temperature. Similarly, FIG. 6 shows the thermogravimetricanalysis profiling the thermal stability of natural graphene 601,thinned graphite 602 and thinned graphene-graphite composite 603. Thefigure shows that the graphene-graphite composite 603 has a higherstability than natural graphite 601 and decomposes at a highertemperature.

In some embodiments, the functionalized graphene and/or thinned graphiteare capable of dispersing into metals and/or oxides to form metal oroxide composites that have several useful properties for applications.For example, such graphene and/or thinned graphite can be mixed withmetals such as silicon, titanium, copper, etc., to producegraphene-metal composites that have high thermal conductivity, and assuch can be suitable for applications such as in cooling systems, etc.As another example, such graphene and/or thinned graphite can be mixedwith metal oxides such as but not limited to titanium oxides andtitanium dioxides to produce graphene-metal oxide composites withimproved thermal and/or electrical conductivities. FIG. 7 shows plots ofFourier transform infrared spectroscopy of silicon-graphene (top panel)and titanium dioxide-graphene (bottom panel) composites representing ahigh degree of dispersion.

In some embodiments, higher concentration of the oxidizer can lead torapid delamination and/or oxidation of graphite edges and the thinningof graphite (or conversion of graphite into graphene). Further, extrametal hydroxide salt can increase the conductivity of the mixture,allowing for a faster rate of graphite thinning and/or graphite-graphenecomposite formation. However, it can also lead to higher concentrationof hydrogen by-products and higher risk of explosion inside the jars. Assuch, gentle forces and good control of the chemistry of the mixture andthe electrostatic charge formation, such as careful ventilation ofgasses inside the jar using safety valves, etc., can be beneficial inincreasing the safety of the wet ball milling process, in particular forlarge scale processes.

In some embodiments, once the final product of single layers ofgraphene, thinned graphite, graphene-graphite composites, and/or thelike is obtained, post-processing washing can remove by-products orresidues to increase quality of the product. For example, diluted/weakacid washing and drying can remove metallic ions, surfactants, metalsalts, etc., from single and/or few layer graphene and render theproduct suitable for several applications where high purity graphene isneeded such as but not limited to solar cells, Li-ion batteries,supercapacitors, flexible displays, etc. For example, the washing couldbe performed with water, HCl, ethanol, etc., followed by vacuumfiltration, centrifugation, sonication, vacuum drying, etc. In someembodiments, the result could be a high-purity thinned graphite/graphene(e.g., 99% purity by weight) with little or no crystalline imperfection,and/or high thermal stability, allowing the use of such products in awide range of applications including battery applications such asalkaline batteries, natural additives in fire retardant applications,lubrication applications, and/or the like. In some embodiments, theexfoliated graphite/graphene product can be mixed with metals such asbut not limited to titanium, copper, and silicon to improve the thermalconductivity of the end product. Further, it can also be mixed withmetal oxides such as but not limited to titanium dioxide to improve theproduct's thermal conductivity and electrical conductivity.

Experimental Characterization of Thinned Graphite and Few-Layer Graphene

Some embodiments of the wet ball milling process disclosed herein havebeen employed to produce thinned graphite, few-layer graphene (FLG),graphene-graphite composites, and/or oxidized few-layer graphene (i.e.,graphene partially oxidized (GPO)). Some of the resulting products canbe conveniently classified into the following classes or grades:

-   -   Grade A: A few-layer graphene powder of about 3 to 4 graphene        layers and lateral size (e.g., flake diameter) of about 5 μm to        20 μm. This few-layer graphene has been found to exhibit highly        activated edges and low defect density.    -   Grade B: A few-layer graphene powder of about 2 to 3 graphene        layers and lateral size (e.g., flake diameter) of about 0.5 μm        to 5 μm. This few-layer graphene has been found to exhibit        highly activated edges and low defects.    -   Grade C: A few-layer graphene powder with similar properties as        Grade A, but with moderately activated edges.    -   Grade D: A few-layer graphene powder with similar properties as        Grade B, but with moderately activated edges.    -   Grade E: A graphite/graphene composite of thinned/few-layer        graphene (e.g., similar to Grade B) bonded to larger crystalline        graphite.    -   Grade F: A highly activated few-layer graphene of about 1 to 2        graphene layers and lateral size (e.g., flake diameter) of about        0.2 μm to 0.5 μm. In some embodiments, some of the edge hydroxyl        groups have oxidized to form carbonyl groups.

These graphene-based products are suitable for a wide range ofapplications, including lubricants, coatings, paints, compositematerials, thermal management and energy applications. For example,Grade F products are capable of readily dispersing in water and/ororganic solvents, making them excellent candidates to replace grapheneoxide in many applications. Further, Grade F graphene layers can besuitable for mixing with polymers, paints, lubricants, heat transferfluids, and/or the like.

In some embodiments, the characterization of the products of the wetball milling process disclosed herein includes the determination ofvarious physical, chemical, etc., properties of the products. Examplesof these properties include lateral size, defect density, thickness,edge activation and extent of reduction of crystalline graphite intographene layers as measured by, for example, the proportion of graphene(i.e., single layer) to graphite (non-single layers) content.

With respect to lateral size of the graphene-based products, well knownexperimental techniques such as scanning electron microscopy (SEM) couldbe used to capture images of the products for analysis. For example,FIGS. 8A-8F shows example SEM images of Grade A few-layer graphene (FIG.8A), Grade B few-layer graphene (FIG. 8C), Grade C few-layer graphene(FIG. 8B), Grade D few-layer graphene (FIG. 8D), and Grade Egraphene-graphite composite (FIGS. 8E and 8F). The figures suggest thatthe FLG of the shown grades comprise flake shaped particles with adistribution of sizes. For example, Grade B FLG are thin layeredstructures stacked together. An analysis of the SEM images reveal theFLGs of each grade are composed of different sized flakes or particles.For example, Grades A and C have been found to include particles orflakes ranging in lateral size from about 5 μm to about 20 μm (FIG. 9A),Grades B and D include particles ranging in lateral size from about 0.5μm to about 5 μm (FIG. 9B), and Grade E includes particles ranging inlateral size from about 0.5 μm to about 10 μm.

With respect to thickness and defect density of the graphene-basedproducts of the wet ball milling process, in some embodiments, Ramanspectroscopy can be used to characterize these properties. For example,in some of the experimental embodiments described herein, visible light(e.g., 532 nm wavelength light corresponding to 2.33 eV energy) havebeen used to obtain Raman spectra for bulk graphite 1001, Grade A FLG1002, Grade B FLG 1003, Grade C FLG 1004, Grade D FLG 1005, Grade Egraphene-graphite composite 1006, and Grade F activated graphene 1007,all of which are shown in FIG. 10 . The Raman spectra for all the gradesshow peaks that are the result of in-plane vibrational modes caused byexcitations due to the laser used for the spectroscopy. These peaks orbands include the primary in-plane mode of the so-called G band aroundwavenumber 1580 cm⁻¹, a different in-plane vibration mode of theso-called D band around wavenumber 1300 cm⁻¹, and a second-orderovertone of the D band, the so-called 2D band around wavenumber 2700cm⁻¹. In some embodiments, the ratio of the intensity at the G band tothe intensity at the D band good indication of the presence of defectsin the flakes can be used as a measure of the presence of defects in thegraphene-based material being investigated, wherein a small value of theratio indicating large defect presence and vice versa. From the resultsof the Raman spectroscopy (FIG. 10 ), the average value of the ratio forthe FLGs of Grades A, B, C, and D is calculated to be about 20, a largevalue indicating low numbers of defects in the FLGs (and furtherindicating that the FLGs are large-sized).

In some embodiments, the Raman spectra can also be used for determiningthe number of layers, i.e., the thickness, in a few-layer graphene. Forexample, as discussed in Phys. Rev. Lett., 97, 187401 (2006), the entirecontents of which is incorporated herein by reference in its entirety,the 2D peak of Raman spectra changes in shape, width, and position foran increasing number of layers. As such, the position, for example, ofthe 2D peak can be used in determining the number of layers. Using thetechniques discussed in Journal of Physics: Conference Series 109 (2008)012008, the entire contents of which is incorporated herein by referencein its entirety, a two peaks deconvolution using Lorentzian functionswas chosen. The fact that this two peaks deconvolution was possible, asshown in FIGS. 11A-11G, indicates that the number of layers was greaterthan two. A careful analytical comparison of the 2D peaks amongst thedifferent grade FLGs reveals that the 2D peak shifts from a higherwavenumber for crystalline graphite with large number of graphene sheetsto a lower wavenumber for few-layer graphene such as Grade E FLGs, asshown in FIGS. 12A-B. Comparison of the 2D peak positions for thedifferent grades with the data provided in Chem. Comm., 2011, 47,9408-9410, the entire contents of which is incorporated herein byreference in its entirety, allows one to establish the number of layersin the FLGs and graphene-graphite composite of Grades A-E and bulkgraphite. FIG. 13 provides a compact view of the number of layers of theFLGs and graphene-graphite composites of Grades A-E and bulk graphite inrelation to the 2D peak positions. A tabulation of the 2D peaks and thenumber of layers for each grade is given below:

NanoXplore 2D_(A) peak 2D_(B) peak Number of Sample position positionlayers Graphite 2682.03 cm⁻¹ 2716.67 cm⁻¹ >=10 Grade A 2665.26 cm⁻¹2700.34 cm⁻¹ 2 to 3 Grade B 2666.09 cm⁻¹ 2703.01 cm⁻¹ 4 to 5 Grade C2666.28 cm⁻¹ 2702.82 cm⁻¹ 2 to 3 Grade D 2666.37 cm⁻¹ 2699.72 cm⁻¹ 4 to5 Grade E 2664.52 cm⁻¹ 2697.76 cm⁻¹ Some 2 to 3 flakes

In some embodiments, the G peak of the Raman spectra can also be used inevaluating the number of layers in the FLGs and the graphene-graphitecomposites. According to J. Raman Spectrosc. 2009, 40, 1791-1796, theentire contents of which is incorporated herein by reference in itsentirety, an empirical evaluation of the number of layers can also bedetermined from G peak position using the equation

$N = {N_{Graphite} - \frac{K}{1 + n^{1.6}}}$

where N is the wavenumber of the G peak of the FLG or graphene-graphitecomposite, n is the number of layers, N_(Graphite) is the wavenumber ofbulk graphite corresponding to large value of n (e.g., n>10), and K acalculated coefficient. Using the wavenumber for the aforementioned Gpeaks of the Grade A-E FLGs and graphene-graphite composites, andsetting the wavenumber of bulk graphite N_(Graphite) to be about 1579.38cm⁻¹, the coefficient K was calculated to be about 54±3. In someembodiments, this method of evaluation gives some coherent results forGrades B, D and E with about 2 to 3 layers; however, in someembodiments, a small difference can be observed for Grades A and Bindicating up to 4 layers (e.g., instead of 3). FIG. 14 providescalculated values for the number of layers of the FLGs andgraphene-graphite composites of Grades A-E and bulk graphite in relationto the G peak positions. In view of experimental and/or simulationerrors that occur in the above two methods of determining the number oflayers in samples of Grades A-E, in some embodiments, a reasonabledetermination of about 2-3 layers for Grades B, D and E and about 3-4for Grades A and C can be made.

In some embodiments, the wet ball milling processes disclosed herein arecapable of producing thinned graphite (including FLGs) that are edgeactivated. For example, activation of thinned graphite edges leads toappearance of hydroxyl groups (OH⁻) at the edges that serve as chemical“hooks” for the FLGs and composites of Grade A, B, C, D and E in variousamounts. X-ray Photon Spectroscopy (XPS) has been used to characterizethe surfaces and identify the hydroxyl groups of the graphene-basedproducts of Grades A, B, C, D, E and F. FIGS. 15A-15F show the XPSspectra of Grade A (FIG. 15A), Grade B (FIG. 15B), Grade C (FIG. 15C),Grade D (FIG. 15D), Grade E (FIG. 15E) and Grade F (FIG. 15F) with someof the peaks corresponding to the atomic orbitals identified.Deconvolution was performed to semi-quantify the carbon species on thesurface where the same pattern was used for all five grades. Fourintensity peaks were identified:

-   -   Peak from carbon sp² due to graphitic carbon. It can be seen        that this peak is the most intense because graphene is composed        of a vast majority of carbon atoms in sp².    -   Peak from carbon sp^(a) due to tetrahedral bonded carbon. This        carbon species can be found on the edges of the graphene        platelets.    -   Peak from carbon-oxygen (C—O) is due to the hydroxyl groups on        the edges of graphene platelets. This shows that the wet ball        milling process is capable of effectively functionalizing        graphene platelets edges.    -   Peaks from π-π are typical of graphitic carbon and can be        attributed to resonance. The presence can be expected in        graphene because this is a graphitic material.        Integrals, i.e., summation of the intensities of each peak for        each grade are tabulated below, indicating that all six grades        comprise activated edges with hydroxyl groups.

C1s sp3 C1s sp2 C1s C—O C1s C═O C1s π-π * Grade A 10.19 58.85 22.84 08.12 Grade B 9.23 61.71 18.54 0 10.51 Grade C 9.63 61.84 22.61 0 5.92Grade D 10.01 61.95 21.21 0 6.84 Grade E 8.49 59.54 23.69 0 8.28 Grade F14.69 53.19 17.2 3.94 10.98

FIG. 15F shows the deconvoluted XPS Carbon is spectra of Grade F. Themain difference from Grade D is the emergence of a new peak around 287.5eV that can be attributed to carbonyl. Quantification based onintegration of the peaks indicates a 3.94% presence of carbonyl groups(as shown in the table above). Hydroxyl group quantification is lower inGrade F compared to Grades A to E; it is noticeable that the differencecorresponds with the quantification of carbonyl groups. Therefore it canbe deduced that some hydroxyl groups have been oxidized to formcarbonyl.

To characterize the edge activation and other properties of the variousgrades, in some of the experimental embodiments, other techniques suchas Fourier transform infrared spectroscopy by attenuated totalreflection (ATR-FTIR) were performed on the grades. FIG. 16 shows thatall grades exhibit the C—O stretching mode around 1060 cm⁻¹ and the C—OHstretching mode around 1200 cm⁻¹. These modes confirm the presence ofhydroxyl groups over the graphene flakes, including FLGs of Grade E.Around 1600 cm⁻¹ the vibration of graphitic domains is observed for theFLGs and composites of the grades, but not for bulk graphite due to thehigh number of graphitic layers. This is further evidence that FLGs andcomposites of grades A through E comprise few-layers of graphene, unlikethe bulk or large numbers of graphite. The O—H stretching mode around3400 cm⁻¹ has been observed only on the 13.2 (Grade C). This mode wasalso expected on all other grades except Grade E.

FTIR measurements have provided additional supporting evidence as to theXPS detection of the presence of carbonyl groups on the edges of grade FFLGs. For example, FIG. 17 shows the FTIR spectra of grade F FLGs whereseveral significant absorption bands, corresponding to different localenvironments, can be identified:

-   -   around 1100 cm⁻¹ wavenumber, due to the stretching mode of        alkoxy C—O bonds,    -   around 1250 cm⁻¹ wavenumber, due to the epoxy C—O asymmetric        stretching vibrations,    -   around 1400 cm⁻¹ wavenumber, associated with the carboxy O—H        bonds,    -   around 1590 cm⁻¹ wavenumber, corresponding to C═C, from the        non-oxidized sp² carbon bonds,    -   around 1750 cm⁻¹ wavenumber, associated with C—O, stretching        vibrations,    -   around 3200 cm⁻¹ wavenumber, comprising contribution from the        adsorbed water molecules, and    -   around 3430 cm⁻¹ wavenumber associated with the O—H oscillations        in the carboxylic groups, on the edges of graphene planes, as        well as in between the graphene sheets.

These measurements show that carbonyl groups were added to the hydroxylgroups on the edges of the platelets, and in general provide furtherevidence of edge activation of the FLGs and composites of grades A-F.

As have been mentioned above and would be discussed in greater detailbelow, the products of the wet ball milling process disclosed herein canbe used in a diverse set of applications. For some of theseapplications, it may be useful to determine the characteristics of theproducts under different conditions, for example, their thermalstability. In some embodiments, thermal stability may be investigatedvia a thermo gravimetric analysis (TGA) that tracks the thermaltransitions of the materials as a function of temperature, transitionssuch as but not limited to loss of solvent and plasticizers in polymers,water of hydration in inorganic materials, and/or decomposition of thematerial. A TGA analysis was performed for each grade by raising thetemperature of a furnace containing the FLGs or the composites andmeasuring the sample weight. FIG. 18 shows the weight percentage of thesample remaining after mass loss as a function of temperature when thetemperature is raised to 930° C. at 10° C./min rate in air for the FLGsof Grades A and B (1801), Grades C and D (1802), Grade F (1803) andGrade E (1804). For grades A, B, C and D, the degradation starts ataround 690° C., in contrast to 800° C. for graphite and 600° C. for agraphene layer, indicating that these grades comprise few-layer grapheneproducts, agreeing with the results of other measurements such as Ramanspectroscopy. In some embodiments, loss prior to degradation has beenobserved (e.g., at less than 2%) and can be ascribed primarily residuefrom the washing process. For grade F (1803), two weight decreases canbe observed in the TGA data, where at around 250° C., structural water,hydroxyl and carbonyl groups are removed from the powder, and at around592° C., the decomposition of the FLG occurs. This decompositiontemperature is slightly lower than that for Grade D but still veryclose, showing that the pristine nature of the FLG flakes has beenconserved. In general, these results show the heat resistance propertiesof the FLGs produced as a result of the wet ball milling process.

With respect to the graphene-graphite composite of grade E, thedecomposition temperature can be seen to be around 710° C., which ishigher than Grades A, B, C, and D. These results show that thinnedgraphite (e.g., forming the composite) can have strong influence onthermal properties of Grade E, and means that Grade E is more heatresistant than graphene and/or FLGs.

Some explanations for these unique properties come from the differencein synthesis process and consequently morphology of Grade E compositescompares to the FLGs of, for example, Grades A, B, C and D. For example,the synthesis process of Grade E can be divided in two parallelprocesses that give a thinned graphite and a graphene. For example, theSEM image of Grade E in FIG. 8F shows a wide range in particle sizewithin the powder. Some flakes have the same lateral size as Grades B orD (e.g., 1-5 μm) and some are almost millimeter sized. The structure ofGrade E can be described as small graphene flakes sitting on larger,thinned graphite particles, and as a result, this material can havedifferent characteristics than single and/or few-layer graphene.

However, XPS analysis demonstrates that the wet ball milling processdisclosed herein can induce hydroxyl activated edges (FIGS. 15A-15F),allowing for dispersibility of the powder in various medium, bothorganic and water-based. Further, with respect to electricalconductivity, composite graphene-thinned graphite Grade E can beexpected to have a much better conductivity than Grades A, B, C and D,since the number of electrons available is much higher even though thefree electron mobility of graphite (including thinned) is lower comparedto FLGs.

Applications

Currently, monolayer graphene produced by CVD processes and lowerquality graphene are commercially available. However, there are severalissues that render these graphene products unsuitable for severalapplications. For example, the CVD process is realistically not scalablefor large scale production, and the lower quality products containsignificant defects, have small lateral sizes, contain no activatededges, etc. The graphene-based products produced by the wet ball millingprocesses disclosed herein have properties that make them suitable for adiverse set of applications. In some embodiments, the FLGs and thecomposites have low defects, activated edges, relatively large lateraldimensions and/or few layers, and also are dimensionally tunable anddispersive. Some of the applications for which the thinned graphite, theFLGs, graphene-graphite composites, etc., can be used for are listedbelow.

Lubricants

Graphene can provide significant benefits for lubricants in at leastthree ways, including as an additive to improve oil-based lubricants, asa replacement for existing, hazardous additives (e.g., for currentenvironmentally unfriendly lubricant additives such as molybdenumdisulfide or boric acid), and as a replacement for graphite-basedlubricants. As an additive, for example, adding graphene to existingoil-based lubricants provides many advantages including reducingfriction, forming an extremely strong and durable surface layer on thetarget surfaces that can be stable under a wide range of loads andtemperatures, improving lubricants to act as excellent cooling fluidremoving heat produced by friction or from external sources, andimproving lubricants to protect surfaces from the attack of aggressiveproducts formed during operation (including anti-corrosion protection).For example, a test by lubricant specialists of the graphene basedproducts produced by the processed disclosed herein has shown a very lowloading of about 1 mg/mL in paraffin oil, the coefficient of frictionwas reduced by about 66%.

Graphite is a commonly used solid lubricant, especially in moist air(but may not protect the surface from corrosion). It has been shown thatgraphene works equally well in humid and dry environments. Furthermore,graphene is able to drastically reduce the wear rate and the coefficientof friction (COF) of steel. The marked reductions in friction and wearcan be attributed to the low shear and highly protective nature ofgraphene, which also prevents oxidation of the steel surfaces whenpresent at sliding contact interfaces.

Using the graphene-based products of the wet ball milling processesdisclosed herein as additives, even in minute amounts such as between1.0% and 0.1% of graphene by weight as an additive, the above-mentionedadvantages of graphene in lubricants can be realized. Further, theminute amount creates minimal or no impact to existing manufacturingprocesses, also allowing for a compact product development andintroduction timeline. The higher quality of the graphene-based productsallow for minute amounts to achieve significant improvements inlubricant performance, which partly is the result of the ability to tunethe dimensions of the graphene nanoplatelets and their dispersiveness inother materials. In some embodiments, it is useful to have the abilityto tune the dimensions of the graphene nanoplatelets depending on thetarget application. The dimensions can be lateral size (e.g.,diameter)—larger nanoplatelets generally provide more continuous surfaceprotection, and dispersion—smaller particles are often more easilydispersed in the target lubricant.

Coatings and Paints

Coatings are used to improve the surface properties of a substrate,properties such as corrosion resistance, durability, wettability, andadhesion. Paints are a special category of coating, used to protect,beautify and reduce maintenance requirements. Graphene, alone or as partof a composite, displays excellent characteristics for the coatingindustry including water and oil resistance, extraordinary barrierproperties (including anti-corrosion), superb frictional properties, andhigh wear resistance. In addition, graphene has excellent electrical andthermal properties and thin layers of graphene are opticallytransparent. Further, graphene based coatings exhibit excellentmechanical properties as well as being largely or completely impermeableto gases, liquids and strong chemicals. Examples include using graphenebased paint to cover glassware or copper plates that may be used ascontainers for strongly corrosive acids. Other areas of applicationsinclude industries in medicine, electronics, nuclear and shipbuilding,were identified. The graphene based products of the wet ball millingprocesses of this disclosure can be used to accomplish theaforementioned applications of graphene in as a coating additive.

Composite Materials

Composite materials are made from two or more different materials thatare combined together to create a new material with characteristicsdifferent from the individual components. The goal is to create asuperior new material with improved performance in some aspect such asstrength, less weight or lower cost. Graphene, with its unprecedentedarray of material characteristic improvements, is a natural candidatefor use in advanced composite materials. Leading candidates forgraphene-based composites include structural and skin components forairplanes, cars, boats and spacecraft. In these applications, graphenecan be used to increase thermal conductivity and dimensional stability,increase electrical conductivity, improve barrier properties, reducecomponent mass while maintaining or improving strength, increasestiffness and toughness (impact strength), improve surface appearance(scratch, stain and mark resistance), and increase flame resistance. Thegraphene based products including the graphene-graphite composite andthe edge activated FLGs discussed in this disclosure can be used justfor such applications. Examples of the effects of these products includeimproving mechanical/structural properties, thermal and/or electricalconductivity, wear resistance and long lasting surface properties,anti-corrosion and anti-erosion properties, particularly under dynamicloads; and electromagnetic shielding.

Thermal Management

The demand for innovative thermal management materials and adhesives isdriven by the harmful heat generated by ever-shrinking electroniccomponents and systems in all areas of the electronics market, includingaerospace, automotive, consumer, communications, industrial, medical,and military. In recent years, there has been an increasing interest innew and advanced materials for thermal interface materials (TIM) andheat conduction. The important basic factors to consider when selectinga thermal interface material (TIM) are a high, thermally conductiveinterface material that is as thin as possible, a material that forms anexcellent thermal interface with a wide range of materials and amaterial that eliminates voids or air pockets between the heatgenerating device surface and the heat sink surface. The graphene basedproducts disclosed in this disclosure possess superior electricalconductivity, and ultra-low interfacial thermal resistance againstmetal, and as such are suitable for thermal management applications.Further, the edge activation facilitates mixing with other materialssuch as existing TIM materials.

Energy

Graphene-based nanomaterials have many promising applications inenergy-related areas. Graphene improves both energy capacity and chargerate in rechargeable batteries; graphene makes superior supercapacitorsfor energy storage; transparent and flexible graphene electrodes maylead to a promising approach for making solar cells that areinexpensive, lightweight and manufactured using roll-to-roll techniques;graphene substrates show great promise for catalytic systems in hydrogenstorage for automotive and grid storage applications.

The graphene based products of the present disclosure can beparticularly suited to electrode-based energy solutions, andspecifically for improving the performance of Li-ion anodes. CurrentLi-ion anodes are made from graphite while new generation anodes arebeing fabricated from composites such as silicon-carbon. Graphenecomposite anodes, fabricated using a composite of graphene and metals,oxides or polymers, can have even better performance in the areas ofpower density, energy density, and battery cycle life. Further, graphenebased composites can often provide production advantages while alsohelping to address the overheating and swelling problems oftenexperienced by advanced battery cells. In addition, the excellentthermal and electrical conductivity, and the ability to mix and formcomposites with a wide range of other materials, of the graphene basedproducts of the present disclosure allow for its use in batterytechnologies, including effecting improvements in the performance ofLi-ion batteries.

While various embodiments of the system, methods and devices have beendescribed above, it should be understood that they have been presentedby way of example only, and not limitation. Where methods and stepsdescribed above indicate certain events occurring in certain order,those of ordinary skill in the art having the benefit of this disclosurewould recognize that the ordering of certain steps may be modified andsuch modification are in accordance with the variations of theinvention. For example, the non-aqueous electrolyte can also include agel polymer electrolyte. Additionally, certain of the steps may beperformed concurrently in a parallel process when possible, as well asperformed sequentially as described above. The embodiments have beenparticularly shown and described, but it will be understood that variouschanges in form and details may be made.

1-81. (canceled)
 82. A composition, comprising: a plurality of few layergraphene particles, the plurality of few layer graphene particles havinga thickness of 1 graphene layer to about 10 graphene layers and anaspect ratio of at least about 50, the composition having a G-bandintensity to D-band intensity ratio between about 14 and about 28,wherein the plurality of few layer graphene particles have a purity ofgreater than about 95% by weight.
 83. The composition of claim 82,wherein the few layer graphene particles have lateral dimension of about500 nm to about 5 μm.
 84. The composition of claim 83, wherein theplurality of few layer graphene particles have an aspect ratio of atleast about
 100. 85. The composition of claim 84, wherein the pluralityof few layer graphene particles have an aspect ratio of at least about250.
 86. The composition of claim 82, wherein the plurality of few layergraphene layers are edge functionalized.
 87. The composition of claim86, wherein the plurality of few layer graphene layers are edgefunctionalized with hydroxyl groups.
 88. The composition of claim 82,wherein the plurality of few layer graphene particles have a lateraldimension in a range of about 500 nm to about 5 μm.
 89. The compositionof claim 82, wherein the plurality of few layer graphene particles areformed from combining a crystalline graphite with a solution, thesolution including at least one of a metal hydroxide salt, an oxidizer,and a surfactant.
 90. A composition, comprising: a plurality of fewlayer graphene particles, the plurality of few layer graphene particleshaving an average lateral dimension of at least about 500 nm and anaspect ratio of at least about 50, the composition having a G-bandintensity to D-band intensity ratio between about 14 and about 28,wherein the plurality of few layer graphene particles have a purity ofgreater than about 95% by weight.
 91. The composition of claim 90,wherein the plurality of few layer graphene particles have a thicknessof less than about 5 nm.
 92. The composition of claim 91, wherein theplurality of few layer graphene particles have an aspect ratio of atleast about
 100. 93. The composition of claim 92, wherein the pluralityof few layer graphene particles have an aspect ratio of at least about250.
 94. The composition of claim 90, wherein the plurality of few layergraphene particles have a thermal stability up to about 690° C.
 95. Thecomposition of claim 90, wherein the plurality of few layer graphenelayers are edge functionalized with hydroxyl groups.
 96. The compositionof claim 90, wherein the plurality of few layer graphene particles areformed from combining a crystalline graphite with a solution, thesolution including at least one of a metal hydroxide salt, an oxidizer,and a surfactant.
 97. A composition, comprising: a plurality of fewlayer graphene particles, the plurality of few layer graphene particleshaving: a thickness of less than about 5 nm, an average lateraldimension of at least about 500 nm, and an aspect ratio of at leastabout 50, wherein the composition has a G-band intensity to D-bandintensity ratio between about 14 and about 28, and wherein the pluralityof few layer graphene particles have a purity of greater than about 95%by weight.
 98. The composition of claim 97, wherein the plurality of fewlayer graphene particles have a thermal stability up to about 690° C.99. The composition of claim 97, wherein the aspect ratio is in a rangeof about 50 to about 1,000.
 100. The composition of claim 97, whereinthe aspect ratio is in a range of about 100 to about
 500. 101. Thecomposition of claim 97, wherein the plurality of few layer graphenelayers are edge functionalized.
 102. The composition of claim 97,wherein the thickness of the plurality of few layer graphene particlesis 1 graphene layer to about 10 graphene layers.
 103. The composition ofclaim 97, wherein the average lateral dimension is at least about 1 μm.104. The composition of claim 97, wherein the plurality of few layergraphene particles are formed from combining a crystalline graphite witha solution, the solution including at least one of a metal hydroxidesalt, an oxidizer, and a surfactant.